the number of scented candles ... x
the number of unscented candles ... y
x + y = 28
$16 * x + $10 * y = $400 ... 16 * x + 10 * y = 400
If you would like to know how many scented and how many unscented candles did the shop sell today, you can calculate this using the following steps:
x + y = 28 ... x = 28 - y
16 * x + 10 * y = 400
____________________
16 * (28 - y) + 10 * y = 400
16 * 28 - 16 * y + 10 * y = 400
448 - 400 = 16 * y - 10 * y
48 = 6 * y /6
y = 48 / 6
y = 8
x = 28 - y = 28 - 8 = 20
Result: The candle shop sold 20 scented candles and 8 unscented candles today.